Raster-Scan Displays

Raster-scan displays are a type of video display technology that has been used for several decades. They work by scanning a beam of electrons across a screen to create an image from individual pixels. Raster-scan displays have been used in a variety of devices, including televisions, computer monitors, and oscilloscopes

The most common type of graphics monitor that uses a cathode ray tube (CRT) is the raster-scan display, which is based on television technology. This system works by sweeping an electron beam across the screen, one row at a time from top to bottom.

As the beam moves across each row, it turns on and off to create a pattern of illuminated spots. The picture definition is stored in a memory area called the refresh buffer or frame buffer, which holds the set of intensity values for all the screen points.

These stored intensity values are then retrieved from the refresh buffer and painted on the screen one row at a time. Each screen point is known as a pixel or pel. The ability of the raster-scan system to store intensity information for each screen point makes it ideal for the realistic display of scenes with subtle shading and color patterns. Other systems, such as home television sets and printers, also use raster-scan methods.

The intensity range for each pixel position on a raster system depends on the system’s capability. In a simple black-and-white system, each screen point can only be on or off, requiring only one bit per pixel to control screen intensity.

Raster-Scan Displays

However, additional bits are necessary when color and intensity variations are possible. High-quality systems can have up to 24 bits per pixel, which can require several megabytes of storage for the frame buffer, depending on the system’s resolution.

For instance, a system with 24 bits per pixel and a 1024 by 1024 resolution would require 3 megabytes of storage for the frame buffer. The frame buffer for a black-and-white system with one bit per pixel is commonly known as a bitmap. In contrast, for systems with multiple bits per pixel, the frame buffer is typically called a pixmap.

Raster-scan displays refresh images at a rate of 60 to 80 frames per second, although some systems can handle higher refresh rates.

Refresh rates are sometimes measured in cycles per second or Hertz (Hz), with one cycle equaling one frame. For example, a refresh rate of 60 frames per second would be described as 60 Hz. At the end of each scan line, the electron beam returns to the left side of the screen to start displaying the next scan line.

This return to the left side of the screen is known as the horizontal retrace of the electron beam. At the end of each frame, which is displayed in 1/80th to 1/60th of a second, the electron beam returns to the top left corner of the screen to begin displaying the next frame. This return to the top left corner is called the vertical retrace.

What are Raster-Scan Displays?

Raster-Scan Displays, also known as Bitmap Displays, are electronic displays that use a scanning pattern to display images. This scanning pattern is called a raster. It is a series of horizontal lines that are scanned from left to right and top to bottom. Each line is composed of pixels, which are tiny dots that make up the image. The pixels are illuminated to create the image on the screen.

How do Raster-Scan Displays work?

Raster-Scan Displays work by using an electron beam to scan the screen from left to right and top to bottom. The electron beam is emitted from an electron gun, which is located at the back of the screen. The beam is focused and directed by electromagnetic coils, which are located around the electron gun. The electron beam scans the screen one line at a time, illuminating the pixels to create the image.

Types of Raster-Scan Displays

There are several types of Raster-Scan Displays available in the market. Here are some of the most common ones:

CRT

Cathode Ray Tube (CRT) is the oldest type of Raster-Scan Display. It uses a vacuum tube and an electron gun to create images on the screen. CRTs are known for their high-quality images and fast refresh rates. However, they are bulky, heavy, and consume a lot of power.

LCD

Liquid Crystal Display (LCD) is the most common type of Raster-Scan Display. It uses a layer of liquid crystals to create images on the screen. LCDs are known for their thin profile, low power consumption, and high-resolution images. However, they have a slower refresh rate compared to CRTs.

LED

Light Emitting Diode (LED) is a newer type of Raster-Scan Display. It uses an array of LEDs to create images on the screen. LEDs are known for their bright colors, high contrast, and energy efficiency. They are commonly used in outdoor advertising displays and large video walls.

Plasma

Plasma Display Panel (PDP) is a type of Raster-Scan Display that uses small cells filled with ionized gas to create images on the screen. Plasma displays are known for their deep black levels, high contrast ratio, and wide viewing angles. However, they are less energy-efficient and have a shorter lifespan compared to other types of Raster-Scan Displays.

Applications of Raster-Scan Displays

Raster-Scan Displays have a wide range of applications in various industries. Here are some of the most common applications:

Computer Monitors

Raster-Scan Displays are commonly used in computer monitors. They provide high-resolution images, fast refresh rates, and vibrant colors. They are used in both personal and professional settings, such as gaming, graphic design, and video editing.

Television Screens

Raster-Scan Displays are also used on television screens. They provide high-quality images and a wide range of colors. They are commonly used in homes, hotels, and other entertainment venues.

Medical Imaging

Raster-Scan Displays are used in medical imaging devices, such as X-ray machines, CT scanners, and ultrasound machines. They provide accurate and high-resolution images, which are crucial for diagnosing and treating medical conditions.

Gaming

Raster-Scan Displays are popular among gamers. They provide fast refresh rates, high-resolution images, and vibrant colors, which enhance the gaming experience.

Advertising

Raster-Scan Displays are commonly used in outdoor advertising displays and large video walls. They provide bright and high-contrast images, which are easily visible from a distance.

Advantages of Raster-Scan Displays

Raster-Scan Displays offer several advantages over other types of displays, such as:

  • High-quality images
  • Vibrant colors
  • Fast refresh rates
  • Wide viewing angles
  • High contrast ratio

Disadvantages of Raster-Scan Displays

Raster-Scan Displays also have some disadvantages, such as:

  • Limited lifespan (especially for CRT and Plasma displays)
  • High power consumption (especially for CRT displays)
  • Slow response time (especially for LCD displays)

Future of Raster-Scan Displays

As technology advances, Raster-Scan Displays are also evolving. Manufacturers are developing new technologies to improve the quality, performance, and energy efficiency of Raster-Scan Displays. Some of the emerging technologies include Quantum Dot Displays, MicroLED Displays, and Organic LED Displays.

Conclusion

Raster-Scan Displays are electronic displays that use a scanning pattern to display images. They are used in various industries, such as computers, televisions, medical imaging, gaming, and advertising. They offer high-quality images, vibrant colors, and fast refresh rates. However, they also have some disadvantages, such as limited lifespan and high power consumption. As technology evolves, new types of Raster-Scan Displays are emerging, which promise to improve the quality and energy efficiency of electronic displays.

What is a raster-scan display and how does it work?

A raster-scan display is the most common type of graphics monitor that uses a cathode ray tube (CRT). It works by sweeping an electron beam across the screen, one row at a time from top to bottom. As the beam moves across each row, it turns on and off to create a pattern of illuminated spots. The picture definition is stored in a memory area called the refresh buffer or frame buffer, which holds the set of intensity values for all the screen points.

What is the difference between a black-and-white system and a color system on a raster-scan display?

In a simple black-and-white system, each screen point can only be on or off, requiring only one bit per pixel to control screen intensity. However, additional bits are necessary when color and intensity variations are possible. High-quality systems can have up to 24 bits per pixel, which can require several megabytes of storage for the frame buffer, depending on the system’s resolution.

What is the refresh rate of a raster-scan display?

Raster-scan displays refresh images at a rate of 60 to 80 frames per second, although some systems can handle higher refresh rates. Refresh rates are sometimes measured in cycles per second or Hertz (Hz), with one cycle equaling one frame. For example, a refresh rate of 60 frames per second would be described as 60 Hz.

What is the horizontal retrace and vertical retrace on a raster-scan display?

At the end of each scan line, the electron beam returns to the left side of the screen to start displaying the next scan line. This return to the left side of the screen is known as the horizontal retrace of the electron beam. At the end of each frame, the electron beam returns to the top left corner of the screen to begin displaying the next frame. This return to the top left corner is called the vertical retrace.

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